The invention relates to a method and device to automatically take a picture of a person's face.
DE 42 38 743 A1, published May 19, 1994, discloses a controlling device for a videophone where two portrait cameras are used. A precondition for camera functioning is that the face is close to the camera. Thus, from the start, the face fills a large area of the camera image. The person operating the device first has to position the face accurately in front of one of the cameras. This generates a video image which is stored by an image memory. The actual picture taken subsequently is compared with the image in the form of a reference image stored in the image memory. If the position of the image changes, a correction signal is generated accordingly, with the camera following. In this way, the position of the last image is compared with the position of the new picture, with the camera being controlled accordingly. The second portrait camera is not activated until the range covered by the first camera supplies an unfavorable viewing angle for a reproduction. For change-over purposes, use is made of the deflection angle of the respective camera in action. The change-over takes place when the deflection angle exceeds a certain value. To ensure accurate functioning, it is necessary, first, to affect a manual setting operation. Subsequent control takes place in such a way that the camera follows the subject after its displacement. However, this can only take place in a narrow range. If the subject or face leaves the effective range, it is necessary for a new positioning operation to take place in front of one of the two cameras as well as a manual presetting operation because there is no reference image suitable for subsequent controlling purposes.
DE 31 46 552 C2, published Nov. 17, 1983, discloses a device with two cameras with different image angles. The camera with the smaller image angle serves as a search camera by means of which an observer searches an observation range. Such a device is used for military purposes and serves to possibly identify camouflaged objects in the far distance by means of the teleoptics of the camera with the small image angle. In addition to the image produced by the camera with the small image angle and a correspondingly small imaging range, a survey picture is produced which shows the surroundings of the image detail. If the viewing range of the camera with the small image angle is changed, the position of a marking indicating to the viewer the alignment of the search camera (camera with the small image angle) in the survey picture changes at the same time. In consequence, the two cameras are always moved jointly. For this purpose, the cameras are arranged in a joint adjusting device which is rotatable vertically and horizontally.
EP 05 78 508 A2, published Jan. 11, 1994, discloses a device with a built-in video camera which may be pivoted and inclined by actuators. For the user, this device practically constitutes a standard video camera having a special feature in that any faces positioned in the vicinity in front of the picture taking optics are automatically looked at by the camera. Inside the camera, an image processing device is provided in which a simple abstract face model is stored. The model substantially consists in assuming an image region which is characterized by a certain hue and which, upwardly, is delimited by a second image region with a dark grey color value (hair region). However, the device is effective only if the face is positioned almost completely in the viewing range of the camera. This results in a conflict of objectives of, on the one hand, achieving a high-resolution face image and, on the other hand, of keeping the scale of the image small enough for the tracking mechanism not to break down. In consequence, the device described in the above publication can function satisfactorily only in those cases where the face is positioned closely in front of the camera within a narrowly delimited region, as is the case with video telephones or video conference work stations.